/* ============================================
   About Vector Database — Light theme
   Khaki + Almond + Isabelline + Charcoal + Desert Sand
   Corporate minimalist · Full width · Sharp
   ============================================ */

:root {
  /* Very light theme: Khaki, Almond, Isabelline, Charcoal, Desert Sand */
  --isabelline: #FCFBFA;
  --almond: #FAF8F6;
  --almond-deep: #F5F2EF;
  --khaki: #C3B091;
  --khaki-light: rgba(195, 176, 145, 0.25);
  --charcoal: #36454F;
  --desert-sand: #EDC9AF;
  --charcoal-soft: rgba(54, 69, 79, 0.85);
  --charcoal-muted: rgba(54, 69, 79, 0.6);
  --charcoal-light: rgba(54, 69, 79, 0.4);
  --khaki-border: rgba(195, 176, 145, 0.35);
  --desert-sand-hover: #E5B89A;
  --white: #FFFFFF;

  --bg-page: var(--isabelline);
  --bg-card: var(--white);
  --bg-elevated: var(--almond);
  --bg-chapter: var(--white);
  --text-primary: var(--charcoal);
  --text-secondary: var(--charcoal-soft);
  --text-muted: var(--charcoal-muted);
  --accent: var(--charcoal);
  --accent-hover: var(--desert-sand-hover);
  --border: var(--khaki-border);
  --cta-bg: var(--charcoal);
  --cta-text: var(--white);
  --cta-hover-bg: var(--desert-sand);
  --cta-hover-text: var(--charcoal);
  --hero-accent: var(--khaki);
  --card-hover-border: var(--khaki);
  --chapter-accent: var(--khaki-light);

  --radius: 0;
  --radius-sm: 0;
  --font-sans: "Poppins", system-ui, sans-serif;
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;
  --header-h: 64px;
  --content-padding: 1.5rem;
  --content-padding-lg: 2.5rem;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.6;
  color: var(--text-primary);
  background: var(--bg-page);
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--accent);
  text-decoration: none;
}

a:hover {
  color: var(--charcoal);
  text-decoration: underline;
}

.container {
  width: 100%;
  max-width: 100%;
  margin: 0 auto;
  padding: 0 var(--content-padding-lg);
}

@media (min-width: 1200px) {
  .container {
    padding-left: var(--content-padding-lg);
    padding-right: var(--content-padding-lg);
  }
}

/* ============================================
   Header
   ============================================ */

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-h);
  background: var(--bg-page);
  border-bottom: 1px solid var(--border);
}

.header-inner {
  width: 100%;
  max-width: 100%;
  margin: 0 auto;
  padding: 0 var(--content-padding-lg);
  height: 100%;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: var(--space-md);
}

/* Left: logo image (round, charcoal bg blends with header) */
.header-logo {
  justify-self: start;
  display: flex;
  align-items: center;
  text-decoration: none;
  color: var(--text-primary);
}

.header-logo:hover {
  color: var(--charcoal);
  text-decoration: none;
}

.header-logo-img-wrap {
  display: block;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  overflow: hidden;
  background: var(--charcoal);
  flex-shrink: 0;
}

.header-logo-img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.logo-icon {
  color: var(--charcoal);
  font-size: 1.25rem;
  font-weight: 700;
}

/* Center: site name */
.header-title {
  justify-self: center;
  font-family: var(--font-sans);
  font-weight: 600;
  font-size: 1rem;
  color: var(--text-primary);
  text-decoration: none;
  letter-spacing: -0.02em;
  white-space: nowrap;
}

.header-title:hover {
  color: var(--charcoal);
  text-decoration: none;
}

/* Right: hamburger + nav dropdown */
.header-actions {
  justify-self: end;
  position: relative;
  display: flex;
  align-items: center;
}

.header-menu-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  padding: 0;
  margin: 0 -8px 0 0;
  background: transparent;
  border: none;
  color: var(--text-primary);
  cursor: pointer;
  font-size: 1.5rem;
  line-height: 1;
  border-radius: 4px;
  transition: background 0.2s, color 0.2s;
}

.header-menu-toggle:hover {
  background: var(--almond);
  color: var(--charcoal);
}

.header-menu-toggle[aria-expanded="true"] .header-menu-toggle-icon {
  transform: rotate(90deg);
}

.header-menu-toggle-icon {
  display: block;
  transition: transform 0.2s ease;
}

/* Nav: hidden by default, toggled by hamburger */
.main-nav {
  position: absolute;
  top: 100%;
  right: 0;
  margin-top: 4px;
  min-width: 200px;
  padding: var(--space-sm);
  background: var(--bg-page);
  border: 1px solid var(--border);
  border-radius: 6px;
  box-shadow: 0 8px 24px rgba(54, 69, 79, 0.12);
  display: none;
  flex-direction: column;
  gap: 0;
  z-index: 200;
}

.site-header.nav-open .main-nav {
  display: flex;
}

.main-nav a {
  display: block;
  padding: var(--space-sm) var(--space-md);
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 500;
  text-decoration: none;
  border-radius: 4px;
}

.main-nav a:hover {
  color: var(--text-primary);
  background: var(--almond);
  text-decoration: none;
}

/* WordPress menu (ul) inside .main-nav */
.main-nav .nav-menu {
  display: flex;
  flex-direction: column;
  gap: 0;
  list-style: none;
  margin: 0;
  padding: 0;
}

.main-nav .nav-menu li {
  margin: 0;
}

.main-nav .nav-menu a {
  display: block;
  padding: var(--space-sm) var(--space-md);
}

/* ============================================
   Hero
   ============================================ */

.hero {
  position: relative;
  min-height: 70vh;
  display: flex;
  align-items: center;
  padding: var(--space-3xl) var(--content-padding-lg);
  overflow: hidden;
  background: var(--bg-page);
}

.hero-bg {
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, var(--almond) 0%, var(--bg-page) 50%);
  pointer-events: none;
}

.hero-content {
  position: relative;
  z-index: 1;
  width: 100%;
  max-width: 100%;
  margin: 0 auto;
  text-align: left;
}

.hero-label {
  font-family: var(--font-sans);
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--charcoal-muted);
  margin: 0 0 var(--space-md);
}

.hero-title {
  font-family: var(--font-sans);
  font-size: clamp(1.85rem, 4.5vw, 2.75rem);
  font-weight: 600;
  line-height: 1.25;
  margin: 0 0 var(--space-lg);
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

.hero-title .highlight {
  color: var(--charcoal);
  font-weight: 600;
  border-bottom: 2px solid var(--hero-accent);
}

.hero-lead {
  font-size: 1.05rem;
  color: var(--text-secondary);
  max-width: 52ch;
  margin: 0 0 var(--space-xl);
  line-height: 1.65;
  font-weight: 400;
}

.hero-cta {
  display: inline-block;
  padding: var(--space-md) var(--space-xl);
  font-family: var(--font-sans);
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--cta-text);
  background: var(--cta-bg);
  border: 1px solid var(--charcoal);
  border-radius: var(--radius);
  text-decoration: none;
  transition: background 0.2s, color 0.2s, border-color 0.2s;
}

.hero-cta:hover {
  background: var(--cta-hover-bg);
  color: var(--cta-hover-text);
  border-color: var(--khaki);
  text-decoration: none;
}

.hero-visual {
  position: absolute;
  inset: 0;
  pointer-events: none;
}

.vector-grid {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(var(--khaki-border) 1px, transparent 1px),
    linear-gradient(90deg, var(--khaki-border) 1px, transparent 1px);
  background-size: 32px 32px;
  opacity: 0.25;
  mask-image: linear-gradient(180deg, transparent 0%, black 30%, black 70%, transparent 100%);
}

/* ============================================
   About section
   ============================================ */

.about {
  padding: var(--space-3xl) 0;
  border-top: 1px solid var(--border);
  background: var(--bg-page);
}

.section-title {
  font-family: var(--font-sans);
  font-size: 1.5rem;
  font-weight: 600;
  margin: 0 0 var(--space-xl);
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

.about-content {
  max-width: 65ch;
}

.about-content p {
  margin: 0 0 var(--space-lg);
  color: var(--text-secondary);
}

.about-intro {
  font-size: 1.05rem;
  color: var(--text-primary);
}

.about-content strong {
  color: var(--text-primary);
}

.about-content em {
  color: var(--charcoal);
  font-style: italic;
  border-bottom: 1px solid var(--khaki);
}

/* ============================================
   Explore Topics — chapters as cards, 2-col grid
   ============================================ */

.explore {
  padding: var(--space-3xl) 0;
  border-top: 1px solid var(--border);
  background: var(--almond);
}

.explore .section-title {
  margin-bottom: var(--space-md);
}

.explore-intro {
  color: var(--text-secondary);
  margin-bottom: var(--space-2xl);
  font-size: 0.95rem;
}

.topics-directory {
  display: flex;
  flex-direction: column;
  gap: var(--space-2xl);
}

/* Chapter = one section (e.g. I. Basic Fundamentals) */
.chapter {
  background: var(--bg-chapter);
  border: 1px solid var(--border);
  border-radius: 6px;
  overflow: hidden;
  box-shadow: 0 1px 3px rgba(54, 69, 79, 0.04);
}

.chapter-header {
  display: flex;
  align-items: baseline;
  gap: var(--space-md);
  padding: var(--space-lg) var(--space-xl);
  background: var(--chapter-accent);
  border-bottom: 1px solid var(--border);
}

.chapter-num {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--text-muted);
  letter-spacing: 0.05em;
  flex-shrink: 0;
}

.chapter-title {
  font-family: var(--font-sans);
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text-primary);
  margin: 0;
  letter-spacing: -0.01em;
}

.topic-cards {
  display: grid;
  grid-template-columns: 1fr;
  gap: 0;
  padding: var(--space-sm);
}

@media (min-width: 768px) {
  .topic-cards {
    grid-template-columns: repeat(2, 1fr);
    padding: var(--space-md);
  }
}

.topic-card {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md) var(--space-lg);
  border-radius: 4px;
  text-decoration: none;
  color: inherit;
  transition: background 0.15s;
}

.topic-card:hover {
  background: var(--almond);
  text-decoration: none;
  color: inherit;
}

.topic-card:focus-visible {
  outline: 2px solid var(--charcoal);
  outline-offset: 2px;
}

.topic-card-num {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-muted);
  flex-shrink: 0;
  min-width: 1.5rem;
  text-align: right;
}

.topic-card-title {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text-primary);
  line-height: 1.4;
}

.topic-card-desc {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* ============================================
   Footer
   ============================================ */

.site-footer {
  padding: var(--space-xl) 0;
  border-top: 1px solid var(--border);
  margin-top: var(--space-2xl);
  background: var(--bg-page);
  font-size: 0.8rem;
}

.footer-menus {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--space-xl) var(--space-lg);
  margin-bottom: var(--space-xl);
  padding-bottom: var(--space-xl);
  border-bottom: 1px solid var(--border);
}

@media (max-width: 767px) {
  .footer-menus {
    grid-template-columns: repeat(2, 1fr);
    gap: var(--space-lg);
  }
}

.footer-menu-col {
  min-width: 0;
}

.footer-menu-list {
  list-style: none;
  margin: 0;
  padding: 0;
  font-size: 0.8rem;
}

.footer-menu-list li {
  margin: 0 0 var(--space-xs);
}

.footer-menu-list li:last-child {
  margin-bottom: 0;
}

.footer-menu-list a {
  color: var(--text-muted);
  text-decoration: none;
}

.footer-menu-list a:hover {
  color: var(--text-primary);
  text-decoration: underline;
}

.footer-text {
  margin: 0;
  font-size: 0.8rem;
  color: var(--text-muted);
  text-align: center;
}

.footer-text p:last-child {
  margin-bottom: 0;
}

.footer-widgets {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-align: center;
  margin-bottom: var(--space-md);
}

.footer-widgets .footer-widget-title {
  font-size: 0.9rem;
  font-weight: 600;
  margin: 0 0 var(--space-sm);
  color: var(--text-primary);
}

/* ============================================
   Responsive
   ============================================ */

@media (max-width: 767px) {
  .container,
  .header-inner {
    padding-left: var(--content-padding);
    padding-right: var(--content-padding);
  }

  .hero {
    min-height: 60vh;
    padding: var(--space-2xl) var(--content-padding);
  }

  .hero-content {
    text-align: left;
  }

  .header-title {
    font-size: 0.9rem;
    max-width: 50vw;
    overflow: hidden;
    text-overflow: ellipsis;
  }

  .main-nav a {
    font-size: 0.85rem;
  }

  .section-title {
    font-size: 1.35rem;
  }

  .topic-cards {
    grid-template-columns: 1fr;
  }
}